Rust Repair Maiden Voyage

My original goal was to stop the rust from spreading without doing a lot of metal replacement. With the extent of the rust I've found, I know the correct fix is to weld in a new lower quarter and a new trunk extension (drop off). However, I don't want to spend the money or time on that this year. Instead I'm going to try a temporary fix that I hope will last a number of years and if/when it fails I'll still be in the same position, namely needing to weld in a new quarter and trunk extension. My new plan is to treat the insides with rust reformer and then patch the holes from the inside with fiberglas (mat and/or woven) and epoxy resin.